At present, a fuel cell system including a fuel cell for receiving a supplied reactant gas (a fuel gas and an oxidizing gas) to generate a power has been suggested and put to practical use. In such a fuel cell system, a reactant gas pipe for allowing the fuel gas supplied from a fuel supply source such as a hydrogen tank to flow to the fuel cell is provided with a regulator which is subjected to on/off control to control the state of the gas (e.g., see Japanese Patent Application Laid-Open No. 2005-310718).